`Vanzieleghem et al.
`
`US006246725B1
`US 6,246,725 B1
`Jun. 12, 2001
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`(54) MULTI-CARRIER TELECOMMUNICATION
`SYSTEM WITH POWER ADAPTATION
`MEANS
`
`0753948
`
`1/1997 (EP) .
`
`OTHER PUBLICATIONS
`
`(75) Inventors: Etienne Vanzieleghem, PerWeZ; Frank
`Cyriel Michel Defoort,
`Kruibeke-Bazel; Peter Paul Frans
`Reusens, Laarne, all of (BE)
`
`“American Nat’l Std. for Telecommunications—NetWork and
`Customer Installation Interfaces— Asymmetric Digital Sub
`scriber Line (ADSL) Metallic Interface” of the American
`Nat’l Stds. Inst., NY, 1995.
`
`(73) Assignee: Alcatel, Paris (FR)
`
`* cited by examiner
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`USC 154(b) by 0 days.
`
`(21) Appl. No.: 09/087,708
`(22) Filed:
`Jun. 1, 1998
`
`Related US. Application Data
`(60) Provisional application No. 60/052,140, ?led on Jul. 10,
`1997'
`Foreign Application Priority Data
`
`(30)
`
`Jun. 2, 1997
`
`(EP) ............................................... .. 97401210
`
`(51) Int. c1.7 ................................................... .. H04L 27/04
`(52) us CL ________________ __
`375/295; 375/222
`(58) Field of Search ........................... .. 375/222 260
`375/295
`9 /93_01. 370/431 435; 439’
`’
`’
`’
`’
`References Cited
`
`(56)
`
`US. PATENT DOCUMENTS
`375/260
`5 479 447 * 12/1995 Chow et al
`375/260
`576107945
`3/1997 Gregg et all """""""""
`5:790:550 * 8/1998 Peeters ............................... .. 370/480
`
`FOREIGN PATENT DOCUMENTS
`
`Primary Examiner—Tesfaldet Bocure
`(74) Attorney, Agent, or Firm—Ware, Fressola, Van Der
`Sluys & Adolphson LLP
`
`(57)
`
`ABSTRACT
`
`A telecommunication transmitter (TU) for a multi-carrier
`transmission system of the Digital Subscriber Line [DSL]
`type and Which includes a coding circuit (MMC) able to
`generate “symbols” derived from carriers (Cl—Cn) modu
`lated by incoming data, and a line driver circuit (LDC) to
`amplify these symbols. When idle data are received, the
`poWer dissipated in the transmitter is reduced because the
`-
`-
`symbols are then merely derived from a feW or even a smgle
`Carrier (the “pilot tone”) instead as from all the available
`carriers. The poWer dissipated is even more reduced because
`the line driver Circuit is formed by a parallel Connection of
`a high voltage but loW ef?ciency (LL) and a loWer voltage
`but higher performance (LH) line ampli?er. The higher
`performance, and thus less poWer consuming, ampli?er
`(LH) is used When idle data are received at the input (IN).
`In a variant, there is only one line ampli?er of Which the
`quiescent current is controlled as a function of the data
`traf?c. In another variant, the number of carriers used by the
`Coding Circuit (MMC) is a function of the mean Iraf?c of
`effective data received.
`
`0753947
`
`1/1997 (EP) .
`
`14 Claims, 3 Drawing Sheets
`
`/ TU
`
`I
`
`|
`|
`
`I
`|
`
`I
`
`|
`|
`
`I
`l
`
`DATA
`SELECTOR
`(as)
`
`ox
`
`'
`I
`1
`I
`I
`I
`I
`;
`
`+
`V we
`
`DATA HANDLING
`CIRCUIT (DHC)
`
`"I
`
`'
`I
`I
`I
`I
`I
`I
`:
`
`" __________________________ —_-"
`
`LX
`
`SYNC
`
`DATA
`
`IN 0
`
`DATA TRAFFIC
`DETECTION CIRCUIT
`(BBC)
`|
`
`
`
`U.S. Patent
`
`Jun. 12, 2001
`
`Sheet 1 013
`
`US 6,246,725 B1
`
`:._.\\
`
`_.o_.._
`
`ozzozéSE
`
`8:3=§__o
`
`Ea
`
`mosaum
`
`as
`
`o_.._.._<EEa
`
`
`
`=_§__ozozamo
`
`Gee
`
`
`
`
`
`U.S. Patent
`
`Jun. 12, 2001
`
`Sheet 2 013
`
`US 6,246,725 B1
`
`
`
`k\\
`
`7 7I2
`
`F|G.2
`
`72542555
`
`52 9E
`
`
` 249250251
`
` '/
`
`\
`
`HF
`
`248g
`
`
`
`U.S. Patent
`
`Jun. 12, 2001
`
`Sheet 3 of3
`
`US 6,246,725 B1
`
`_
`
`
`
`50 ollil. .
`
`
`
`E \\ _r $3 as L_
`_ 5 _ _ “E25 M2: _ " SE55“ _
`
`
`
`u _
`_ _ _ _
`
`_ _
`
`_ _
`
`_ _
`
`_ _
`
`_ _
`
`_ _
`n u
`_ _
`
`_ _
`
`_ g n _ 5:25 25 _ n 555% h _ _
`
`? llllllllllllllllllllllllllllllll | | |_ _ _ _ _ _ _
`
`_ $5: 82 50% _
`
`z
`
`5
`
`
`
`US 6,246,725 B1
`
`1
`MULTI-CARRIER TELECOMMUNICATION
`SYSTEM WITH POWER ADAPTATION
`MEANS
`
`In addition to claiming priority under 35 USC § 119(a)
`from EPO application 97401210.6 ?led Jun. 2, 1997, this
`application also claims the bene?t under 35 USC § 119(e) of
`US. Provisional Application No. 60/052,140, ?led on Jul.
`10, 1997.
`
`TECHNICAL FIELD
`
`The present invention relates to a telecommunication
`transmitter for a multi-carrier transmission system, said
`transmitter including coding means coupled betWeen a trans
`mitter input and a transmitter output and able to modulate a
`plurality of carriers With data received at said transmitter
`input and to derive therefrom symbols Which are transmitted
`toWards said transmitter output.
`
`BACKGROUND OF THE INVENTION
`
`A multi-carrier transmission system including such a
`telecommunication transmitter is already knoWn in the art
`and is for instance a Digital Subscriber Line [DSL] Trans
`ceiver Unit [TU] as de?ned in international standards such
`as, for instance, the Asymmetrical Digital Subscriber Line
`[ADSL] standard. This standard is the “ANSI TI.413—
`American National Standard for Telecommunications—
`NetWork and Customer Installation Interfaces—
`Asymmetric Digital Subscriber Line (ADSL) Metallic
`Interface” of the American National Standards Institute
`[ANSI], NeW York—1995. The digital data received at the
`input of such a known transmitter is grouped into frames
`comprising a predetermined number of bits and Wherefore
`the coding means generates corresponding symbols Which
`are transmitted to a telecommunication line connected to the
`transmitter output. Since the voltage of each symbol may
`have different peak values, the signal voltage transmitted on
`the telecommunication line may vary Within a relatively
`large range. As a consequence, the poWer dissipated in the
`telecommunication transmitter is relatively high because it
`has to support a large value of signal voltage to avoid, or at
`least minimiZe, occasional clipping.
`
`SUMMARY OF THE INVENTION
`
`An object of the present invention is to provide a tele
`communication transmitter of the above knoWn type but
`Whereof the poWer dissipation is dramatically reduced.
`According to the invention, this object is achieved due to
`the fact that said telecommunication transmitter further
`includes carrier selection means adapted to apply said car
`riers to said coding means, and data traf?c detection means
`adapted to detect if idle data are received at said transmitter
`input and, if idle data are detected, to control said carrier
`selection means to apply a predetermined reduced set of said
`carriers to said coding means.
`In this Way, When idle data are received at the transmitter
`input, the symbols generated by the coding means are
`merely derived from a feW carriers instead of from all the
`carriers as it is the case When effective data are applied to the
`transmitter input. The poWer on the line is thereby dramati
`cally reduced, as Well as the relatively high poWer dissipated
`in the coding means and thus in the telecommunication
`transmitter.
`Since the symbols, Which are generated When idle data are
`received at the transmitter input, contain only a feW carriers,
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`the poWer dissipated in the transmitter is reduced. In other
`Words, if the number of carriers drops, the dissipated poWer
`is reduced accordingly.
`Another characteristic feature of the present invention is
`that said predetermined reduced set of carriers comprises
`only one carrier that is applied to said coding means.
`For frequency synchroniZation purposes, the only one
`remaining symbol transmitted on the line can be chosen to
`be derived from a so-called “pilot tone”. The transmission
`system remains thus ef?cient in that it alloWs a fast restart
`oWing to the fact that the synchroniZation on the telecom
`munication line is maintained, While the poWer dissipated is
`dramatically reduced With respect to that of the knoWn
`system.
`In a preferred embodiment, the present invention is fur
`ther characteriZed in that said telecommunication transmitter
`further includes data selection means adapted to apply said
`data to said coding means, and in that said data traf?c
`detection means is further adapted, if idle data are detected,
`to control said data selection means to discard the idle data
`received at said transmitter input.
`As idle data may, in some circumstances, be dummy data,
`the latter could be used by the coding means to modulate the
`feW or single carrier(s) from Which symbols could then be
`derived and transmitted on the telecommunication line.
`HoWever, oWing to the present invention such dummy data
`Would be discarded and the single carrier Will remain
`un-modulated. As a result, the poWer dissipation is then
`minimal.
`It should be noted that the sWitching betWeen symbols
`derived from effective data and symbols derived from idle
`data, and vice-versa, can be fast Whereby the poWer savings
`can be improved.
`Preferably, said telecommunication transmitter operates
`according to a predetermined mapping and modulating
`protocol de?ned by a digital subscriber line [DSL] standard
`such as the Asymmetrical Digital Subscriber Line [ADSL]
`standard, and said symbols derived from said data are
`Discrete Multi-Tone [DMT] symbols.
`It is obvious for a person skilled in the art that the above
`multi-carrier transmission technique is not limited to ADSL
`applications using DMT symbols, but can for instance also
`be used in High speed Digital Subscriber Line [HDSL]
`applications, in Very high speed Digital Subscriber Line
`[VDSL] applications, in Symmetrical Digital Subscriber
`Line [SDSL] applications as Well as in relation With
`Orthogonal Frequency Division Multiplexing [OFDM] and/
`or Discrete Wavelet Multi Tone [DWMT] applications. The
`latter are also multi-carrier transmission techniques differing
`from ADSL in that, for instance for DWMT, the Fourier and
`inverse-Fourier transformers used therein are replaced by
`?lterbanks, Wavelets transformers and/or Discrete Cosine
`Transformers [DCT].
`Also another characteristic feature of the present inven
`tion is that said coding means is adapted to count the number
`of symbols transmitted toWards said transmitter output and
`to transmit at least one synchroniZation symbol after each
`group of N symbols, said synchroniZation symbol being
`derived from a frame of synchroniZation signals received at
`said data selection means, and that said N symbols and said
`one synchroniZation symbol form together a super-frame.
`In case of idle data, and as already mentioned, the
`frequency synchroniZation betWeen the transmitter and a
`receiver at the other end of the telecommunication line is
`maintained oWing to the presence of the pilot tone. By
`sending one synchroniZation symbol for every N symbols,
`
`
`
`US 6,246,725 B1
`
`3
`the framing synchronization is also maintained between the
`transmitter and the receiver.
`The invention is further also characterized in that said
`coding means is adapted to transmit at least one line moni
`toring super-frame after each group of M super-frames, said
`line monitoring super-frame including N symbols and at
`least one synchronization symbol, in that said M super
`frames and said line monitoring super-frame form together
`a hyper-frame, and in that said data traf?c detection means
`is adapted to control said carrier selection means to apply all
`the carriers of said plurality to said coding means during the
`transmission of said line monitoring super-frame.
`In the digital subscriber line transmission, the receiver
`measures the quality of the transmission on the line and
`informs the transmitter about this quality. The measurement
`is performed by means of the line monitor symbols trans
`mitted in the line monitoring super-frame. If the quality of
`the transmission becomes to loW, the receiver may request
`the transmitter to go back to the poWer-up status even if idle
`data are received at the transmitter input.
`Still another characteristic feature of the present invention
`is that said data traf?c detection means is adapted to control
`said data selection means to discard idle data received at said
`transmitter input after idle data has been detected for a
`predetermined period of time.
`In a preferred application, said data received at said
`transmitter input are Asynchronous Transfer Mode [ATM]
`cells.
`Also according to the present invention, the poWer dissi
`pated in the telecommunication transmitter can be even
`more reduced oWing to the characteristic feature that said
`telecommunication transmitter further includes line driver
`means coupled betWeen said coding means and said trans
`mitter output and adapted to amplify the symbols generated
`by said coding means prior to transmit them to said trans
`mitter output, said line driver means comprising the parallel
`connection of a relatively loW ef?ciency line ampli?er and
`a relatively high ef?ciency line ampli?er, that said ampli?ers
`operate in a complementary Way so that only one of said
`ampli?ers is operational at a predetermined time moment,
`and that said data traf?c detection means is further adapted
`to control the operation of said relatively high efficiency line
`ampli?er if idle data are detected, and to control the opera
`tion of said relatively loW ef?ciency line ampli?er else.
`When sending only the pilot tone, the line drive means do
`not need to comprise a class-A or class-AB ampli?er that is
`a high voltage and high performant line ampli?er. It may
`then advantageously be replaced by a loWer voltage and thus
`also less poWer consuming line ampli?er, ie an ampli?er
`With a smaller idle poWer dissipation or a smaller supply
`voltage.
`It is to be noted that this last characteristic feature of the
`present invention is preferably, but not necessary, combined
`With the features mentioned above. It is thus for instance
`possible to have a telecommunication transmitter With line
`driver means comprising the parallel connection of a loW
`ef?ciency line ampli?er and a high ef?ciency line ampli?er
`operating in a complementary Way, but Without carrier
`selection means and possibly data selection means as men
`tioned above.
`In a preferred embodiment, if idle data are detected, said
`one carrier applied to said relatively high ef?ciency line
`ampli?er is a sinusoidal Wave.
`In a variant embodiment, said data traf?c detection means
`is further adapted, if idle data are detected, to control the
`quiescent current of said line driver means in order to reduce
`the poWer consumption thereof.
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`4
`Thereby, instead of changing from line ampli?er as above,
`the poWer consumption may also be reduced by making the
`ampli?er less linear but more ef?cient only for a feW number
`of carriers.
`It is to be noted that, in the tWo lost cases, the quality of
`the symbols derived, e.g., from the pilot tone and transmitted
`on the telecommunication line by the high ef?ciency line
`drive means remains suf?cient to maintain the frequency
`synchronization betWeen the transmitter and the receiver.
`The present invention is also characterized in that said
`data traf?c detection means is further adapted to compute the
`mean traf?c of effective data received at said transmitter
`input over a predetermined period of time, and, accordingly,
`to control said carrier selection means to apply a predeter
`mined reduced set of said carriers to said coding means in
`function of the computed mean traf?c.
`The amount of carriers used by the coding means and their
`poWer is then a function of the data traf?c. By using only the
`number of carriers that are necessary to transmit the effective
`data, and each With less power, ie modulated With less bits
`of the data, instead of alWays using all the carriers When the
`actual data are reduced, the poWer consumption of the
`transmitter is reduced in function of the data traffic. This
`sWitching betWeen high and loW capacity could be done in
`a similar fashion as sWitching betWeen high capacity and
`idle.
`
`BRIEF DESCRIPTION OF THE DRAWING
`The above and other objects and features of the invention
`Will become more apparent and the invention itself Will be
`best understood by referring to the folloWing description of
`an embodiment taken in conjunction With the accompanying
`draWings Wherein:
`FIG. 1 represents a telecommunication transmitter TU
`according to the invention;
`FIG. 2 shoWs, at different time scales, a super-frame SF
`and a hyper-frame HF of signals used in the transmitter of
`the FIG. 1; and
`FIG. 3 represents a possible implementation of the line
`driver circuit LDC included in the telecommunication trans
`mitter TU of FIG. 1.
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`The telecommunication transmitter TU shoWn in FIG. 1 is
`of the type “ADSL Transceiver Unit—Central of?ce side”
`[ATU-C] used in multi-carrier transmission system as for
`instance de?ned in the above mentioned Asymmetrical
`Digital Subscriber Line [ADSL] standard. Several of such
`transmitters are mounted in a rack Which is subjected to
`maXimum poWer dissipation requirements. The transmitter
`TU has an input IN Whereat digital data, eg Asynchronous
`Transfer Mode [ATM] cells, are applied, and an output OUT
`Where so-called “symbols” are provided. These symbols are
`the result of, amongst other, mapping and modulating opera
`tions performed by a data handling circuit, generally referred
`to as DHC, on the data received at the input IN. The
`transmitter TU further also includes a line driver circuit LDC
`coupling the data handling circuit DHC to the output OUT
`via a terminal LI and amplifying the symbols prior to
`transmit them on a telecommunication line connected to the
`output OUT. The telecommunication line is a copper tWisted
`pair of Wires Whereof the other end is connected to a remote
`ADSL transceiver (not shoWn).
`It is to be noted that in FIG. 1, the schematic represen
`tation of the ADSL transmitter TU has been largely simpli
`
`
`
`US 6,246,725 B1
`
`15
`
`5
`?ed in order to show only the elements Which are essential
`to understand the scope of the invention.
`The data received at the input IN is applied to an input
`DATA of a data selector DS forming part of the data
`handling circuit DHC. The data selector DS has a second
`input SYNC at Which synchronization signals are supplied,
`as Will be eXplained later. An output of DS is connected to
`an input of a mapping and modulating circuit, hereafter
`merely called coding circuit MMC, of Which another input
`is connected to an output of a carrier selector CS. An output
`of the coding circuit MMC is connected to a terminal Li
`further connected to an input of the line driver circuit LDC
`Whereof an output is connected to the transmitter output
`OUT.
`Both MMC and CS form part of the data handling circuit
`DHC. Several carriers C1, .
`.
`.
`, Cp, .
`.
`.
`, Cn, of Which the
`frequencies are spread over the frequency spectrum of the
`Digital Subscriber Line [DSL] system and that may be
`pre-selected amongst a full set of carriers for their good
`transmission qualities for the particular line connected to the
`transmitter TU, are applied to like-named input terminals of
`the carrier selector CS. These carriers are sinusoidal Waves
`and one of them, referred to as Cp, is the so-called “pilot
`tone” that insures the frequency synchroniZation betWeen
`25
`the present transmitter and a receiver included in the ADSL
`transceiver at the other end of the telecommunication line.
`The data selector DS and the carrier selector CS are
`controlled by a data traffic detection circuit DDC via a
`terminal LX connected to control terminals DX and CX of
`DS and CS respectively. The incoming data of the transmit
`ter TU is received in DDC via an input thereof that is
`connected to the transmitter input IN. The data traffic
`detection circuit DDC is adapted to detect the type of digital
`data: idle or effective, as Well as the mean traffic of this data,
`received at the input IN. According to the result of this
`detection, DDC controls the selectors DS and CS as Will be
`eXplained beloW.
`If effective data are received at the transmitter input IN,
`and thus also at the data input DATA of the data selector DS,
`the latter circuit groups the bits of the data into “frames”.
`These frames are then transferred to the coding circuit MMC
`that maps them to the carriers C1—Cn received via the carrier
`selector CS. MMC further modulates these carriers C1—Cn
`in function of the results of the mapping thereby generating
`Discrete Multi-Tone [DMT] symbols that are transferred to
`the line driver circuit LDC. It is to be noted that the pilot
`tone Cp is preferably not modulated to ensure the above
`mentioned frequency synchroniZation. The purpose of the
`line driver circuit LDC is to amplify the symbols prior to
`transmit them on the telecommunication line, its operation
`Will be described in more detail later.
`For every N=68 DMT symbols transmitted on the line, at
`least one synchroniZation symbol is sent. To this end, at the
`occurrence of the 69”1 symbol, the data selector DS selects
`its second input SYNC to get the synchroniZation signals
`instead of the data from its ?rst input DATA. As for the data,
`the synchroniZation signals are also grouped into frames by
`the data selector DS. The synchroniZation symbol derived
`from such a frame is used for performing framing synchro
`niZation betWeen the transmitter TU and the receiver at the
`other end of the line. A set of N=68 DMT symbols
`(numbered from 0 to 67) and one synchroniZation symbol
`SS (numbered 68) form together a so-called “super-frame”
`SF as shoWn in FIG. 2.
`Furthermore, after having generated M, e.g. M=256, of
`the above super-frames, the coding circuit MMC generates
`
`35
`
`6
`at least one so-called “line-monitoring super-frame” MSF.
`This special super-frame MSF contains line monitoring
`information used by the receiver to measure the quality of
`the transmission on the line. Aset of M super-frames and one
`or more line monitoring super-frame(s) MSF form together
`a so-called “hyper-frame”. An example of such a hyper
`frame HF With M=256 super-frames SF (numbered from 0
`to 255) and one line monitoring super-frame MSF
`(numbered 0) is shoWn in FIG. 2 at a time period t‘ that is
`larger than the time period t shoWing the super-frame SF in
`the some ?gure. A line monitoring super-frame MSF
`includes N=68 line monitoring symbols and the synchroni
`Zation symbol SS. Each line monitoring symbol being
`generated by applying all the carriers C1 to Cn to the coding
`circuit MMC.
`The operation of the data handling circuit DHC and more
`particularly that of the coding circuit MMC Will not be
`described in more detail here since all the details of the
`functioning of these circuits may be found in the above
`mentioned Asymmetrical Digital Subscriber Line [ADSL]
`standard.
`The poWer dissipated in the transmitter TU if effective
`data are transmitted is of about 3 Watt for 100 milliWatt
`effectively transmitted on the telecommunication line. This
`low efficiency is due to several ADSL requirements such as
`the signal quality requirement. Hereafter Will be explained
`hoW this poWer dissipation Will be reduced in function of the
`traffic on the line.
`If idle data are received at the transmitter input IN, it is
`detected by the data traffic detection circuit DDC Which then
`controls, via the terminal CX, the carrier selector CS to
`alloW only a feW of the carriers C1—Cn to be transferred to
`the coding circuit MMC. By generating symbols that are
`derived from a reduced number of carriers, the poWer
`dissipated in the transmitter TU is dramatically reduced. If
`the set of selected carriers is reduced to one, the pilot tone
`Cp is preferably chosen, With respect to the other carriers
`C1—Cn, as the single remaining carrier because it alloWs to
`maintain the frequency synchroniZation betWeen the trans
`mitter and the receiver.
`In some cases, such as for instance for the transmission of
`ATM cells, the idle data are in fact dummy data that could
`be grouped in frames by the data selector DS and then be
`transferred to the coding circuit MMC. To avoid the gen
`eration of symbols derived from such dummy data, the data
`traffic detection circuit DDC also controls, via the terminal
`DX, the data selector DS to discard any idle data received at
`the input DATA. As a result, no data are then applied to the
`coding circuit MMC.
`In other Words, if idle data are received in the transmitter
`TU and detected by the data traffic detection circuit DDC,
`the latter controls the carrier selector CS and the data
`selector DS in such a Way that the coding circuit MMC
`generates for instance un-modulated symbols, generally
`called “pilot symbols”, instead of the above discrete multi
`tone DMT symbols. The frequency synchroniZation is
`ensured by the choice of the pilot tone Cp forming alWays
`part of the selected carriers, Whilst the frame synchroniZa
`tion is ensured by the synchroniZation symbols SS that are
`generated as usual, ie as With effective data. The line
`monitoring super-frame MSF is composed of idle or effec
`tive symbols but in any case With all the carriers C1 to Cn
`selected and applied to the coding circuit MMC.
`Another parameter that in?uences the poWer dissipation is
`the so-called “crest factor”. The crest factor is the ratio of the
`peak voltage over the Root Mean Square [RMS] voltage on
`
`45
`
`55
`
`65
`
`
`
`US 6,246,725 B1
`
`7
`the telecommunication line and is thus a function of the
`voltage of the symbol transmitted on the line. The crest
`factor of the line signal in a multi-carrier transmission
`system is rather unfavorable. In practice, the poWer dissi
`pated in the transmitter is much higher than the poWer
`actually transmitted on the line. It is knoWn that the loWest
`crest factor is obtained by a sinusoidal Wave Wherefore it is
`then equal to the root of 2. Since all the carriers, including
`the pilot tone, are pure sinusoidal Waves, the pilot symbols
`generated if idle data are detected have the loWest crest
`factor and the poWer dissipated is then minimal.
`The poWer dissipated in the transmitter TU When only
`pilot symbols are transmitted reduces from the above 3 Watt
`to about 1 Watt.
`In a preferred embodiment, the transmitter TU informs the
`receiver that pilot symbols Will be sent in order to avoid
`unnecessary decoding operations at the receiver side. On the
`other hand, in order to avoid excessive sWaps betWeen the
`transmission of DMT symbols and pilot symbols, i.e. sWaps
`betWeen a poWer-up and a poWer-doWn status respectively,
`the data traf?c detection circuit DDC measures the time
`during Which idle data are received at the transmitter input
`IN. DDC then controls the carrier selector CS and the data
`selector DS of the data selection handling DHC so that pilot
`symbols are only generated after a predetermined time of
`idle data being received. In a variant of this implementation,
`the data traffic detection circuit DDC may count a predeter
`mined number of frames of idle data received. The behavior
`of DDC is then the same as When it measures time.
`As already mentioned, the data handling circuit DHC has
`an output terminal LI coupled to a line driver circuit LDC
`that is itself connected to the transmitter output OUT. LDC
`ampli?es the symbols generated by DHC prior to transmit
`them on the telecommunication line. To this end, the line
`driver circuit LDC generally includes a high voltage line
`ampli?er that is generally a class-AB or a class-A ampli?er.
`A draWback of this ampli?er is that it has a loW ef?ciency
`and consumes a lot of poWer. HoWever, in case of transmis
`sion of idle data, i.e. of pilot symbols, such a high voltage
`ampli?er is not necessary. The loW ef?ciency line ampli?er
`may then advantageously be replaced by a loWer voltage,
`higher performant and thereby less poWer consuming line
`ampli?er. Such an implementation is shoWn in FIG. 3, Where
`a loW ef?ciency line ampli?er LL is coupled in parallel With
`a higher ef?ciency line ampli?er LH betWeen the terminals
`LI and OUT. The operation of the line driver circuit LDC is
`such that only one of the ampli?ers LL or LH operates at a
`predetermined time moment. They are therefore controlled
`by the data traf?c detection circuit DDC via its output
`terminal LX. In more detail, if effective data are transmitted,
`DDC controls the loW performant but high voltage line
`ampli?er LL to operate, While it prevents the symbols to be
`transmitted through the ampli?er LH. On the contrary, if idle
`data, i.e. pilot symbols, are transmitted, DDC prevents the
`ampli?er LL to operate, While it controls the higher perfor
`mant and loWer voltage line ampli?er LH to operate.
`In a variant (not shoWn) of this embodiment, the line
`driver circuit LDC only comprises one, loW efficiency, line
`ampli?er and, if idle data are transmitted, the data traf?c
`detection circuit DDC controls the quiescent current [Iq]
`thereof. Although the line ampli?er is thereby made less
`linear, its poWer consumption is dramatically reduced and
`becomes thus more efficient When only a feW number of
`carriers are uses
`In the tWo last cases, a gain of about 1 Watt may be
`obtained on the poWer consumption. HoWever, the quality of
`
`10
`
`15
`
`25
`
`35
`
`55
`
`65
`
`8
`the signals transmitted on the telecommunication line via the
`high efficiency line ampli?er has to remain sufficient to
`maintain the synchroniZation betWeen the transmitter and
`the receiver. To control this quality, each transmitted hyper
`frame HF includes, as already mentioned, a line monitor
`super-frame MSF that is used by the receiver to measure the
`quality of the transmission. The receiver informs the trans
`mitter about the results of the measurements and, When the
`quality is too loW, the receiver requests the transmitter to go
`back to the poWer-up status, even if only idle data are
`received at the transmitter input.
`Because the poWer dissipated in the transmitter TU is a
`function of the number of carriers used and of the kind of
`symbols transmitted on the telecommunication line, the data
`traffic detection circuit DDC is further designed to measure
`the mean traf?c of the data received at the input IN.
`According to the result of this measurement performed for
`a predetermined time period, the data traf?c detection circuit
`DDC controls, via the terminal CX, the carrier selector CS
`to alloW a reduced set of carriers C1—Cp to be transferred to
`the coding circuit MMC. The number of carriers selected by
`CS is a function of the mean traffic detected. By using only
`the number of carriers that are necessary to transmit the data
`instead of using all the available carriers, as When effective
`data are received, the poWer consumption of the transmitter
`is reduced.
`It is to be noted that the different embodiments and
`variants of the present transmitter as described above may be
`used separately or in combination. For instance, it is possible
`to have a telecommunication transmitter Whereof the poWer
`consumption is reduced oWing to the use of a line driver
`circuit LDC comprising the parallel connection of a loW
`ef?ciency line ampli?er LL and a high ef?ciency line ampli
`?er LH operating in a complementary Way, but Without a
`carrier selector CS and possibly a data selector DS.
`While the principles of the invention have been described
`above in connection With speci?c apparatus, it is to be
`clearly understood that this description is made only by Way
`of eXample and not as a limitation on the scope of the
`invention, as de?ned in the appended claims.
`What is claimed is:
`for a multi
`1. A telecommunication transmitter
`carrier transmission system, said transmitter including cod
`ing means (MMC) coupled betWeen a transmitter input (IN)
`and a transmitter output (OUT) and able to modulate a
`plurality of carriers (Cl—Cn) With data received at said
`transmitter input and to derive therefrom symbols Which are
`transmitted toWards said transmitter output, characteriZed in
`that said telecommunication transmitter (TU) further
`includes carrier selection means (CS) adapted to apply said
`carriers (Cl—Cn) to said coding means (MMC), and data
`traffic detection means (DDC) adapted to detect if idle data
`are received at said transmitter input (IN) and, if idle data are
`detected, to control (CX) said carrier selection means to
`apply a predetermined reduced set (Cp) of said carriers to
`said coding means.
`2. A telecommunication transmitter according to claim 1,
`characteriZed in that said predetermined reduced set of
`carriers comprises only one carrier (Cp) that is applied to
`said coding means (MMC).
`3. A telecommunication transmitter according to claim 2,
`characteriZed in that said one carrier (Cp) is a pilo